An investigation of the harmonic characteristics of transformerexcitation current under nonsinusoidal supply voltage

摘要

This paper investigates the effect of supply voltage harmonics onnthe excitation current of a typical 25 kVA single-phase distributionntransformer. A complete analytical model is developed to calculate thentime domain waveform and the harmonic components of the excitationncurrent. The key findings are: the phase angles of the supply voltagenharmonics determine whether or not those voltage harmonics increase orndecrease the distortion of the input current (with respect to thensinusoidal supply voltage case). A peaked input voltage wave distortednby 3rd, 7th, 11th, etc. harmonic components, or a flattened inputnvoltage wave distorted by 5th, 9th, 13th, etc. harmonics, creates anflattened current (i.e., decreases the current harmonics andndistortion). A flattened input voltage wave distorted by 3rd, 7th, 11th,netc. harmonic components, or a peaked input voltage wave distorted byn5th, 9th, 13th, etc. harmonics, creates a peaked current (i.e.,nincreases the current harmonics and distortion): The 3rd harmonicncomponent in the supply voltage has the highest effect on the currentnharmonics and distortion. The effect of higher voltage harmonicsngradually diminishes with frequency. The magnitudes of the individualncurrent harmonics follow the same decreasing/increasing pattern ofnchanges as does current distortion variation. The correspondingnvariations in harmonic current phase angles is negligible